Chesapeake Bay Plumes - A relatively rare, cold-
advection phenomenon, 3 unusual cases in August 2000



Mini-case 1 - Precipitation enhancement in Virginia Beach 8/14/00

The satellite image shows the bay plume as an enhanced convective line, feeding into the convection over Virginia beach.  The radar images show 2 views of the plumes in reflectivity, and a one-hour precipitation product.

Virginia Beach received over 4 inches of rain through the early morning hours, likely enhanced by a convective bay plume.  Roads along the beach were under water, and a Flash Flood Warning was in effect.

Winds through the boundary layer were from 360 to 030 at >10 knots.  850 Mb temperatures were 10-12C in the IAD and WAL soundings, while Bay water temperatures were 24-26C.


Mini-case 2 - Fair Weather Streamer 8/19/00

These 2 satellite images show a fair-weather Bay plume, similar to what we occasionally see during the cool season.  Again, winds through the boundary layer were from 360 to 040 at >10 knots, and 850 Mb temperatures at IAD and WAL were 10-12C.  Bay water temperatures were about 24C.  The plume can also be seen in radar imagery.


Mini-case 3 - Convective streamer resulting in waterspouts 8/20/00


Some extensive mid and high clouds began to filter into the Chesapeake Bay region shortly after sunrise, and due to the mix of cloud layers, the Bay plume is best viewed with enhanced visible imagery.  The plume is apparent in the first satellite image, extending into northeastern North Carolina.  The successive 2 images show the small elements of enhancement, marking the deeper clouds over the Bay.  The 3rd image shows one enhanced cell over the Bay, right about the time multiple waterspouts were observed off Mathews County.  The 2 radar images show the orientation of the plume, but reflectivity (in clear air mode) indicates just a pinhead of a shower, likely only producing sprinkles.  No radar images in precipitation mode are shown, because the showers could not be detected.  Winds from the surface through the boundary layer were 010-040 at <10 knots, and 850 Mb temperatures were around 9C at IAD and WAL.  Bay water temperatures were around 24C.  Waterspouts were observed near Norfolk by midday, and new cells developed, creating more waterspouts off Mathews County shortly after noon, all associated with non-precipitating convective clouds.



 
 

Chesapeake Bay Plumes - September 2000 Cases,
typical of the transition to the cool season



Mini Case 4 - Classic Cold Air Advection 9/27/00



A strong cold front passed through Virginia and North Carolina during the early morning hours of 9/27.  The surface winds shifted to the north, as 850 Mb temperatures dropped to around 6C.  Water temperatures were around 22C.  The plume was detected in Infrared imagery, Visible imagery, and radar data.


Mini Case 5 - Convective streamer resulting in funnel clouds 9/29/00


A weak piece of upper-level energy was tracking through the region, bringing a reinforcing shot of colder air on 9/29.  Surface winds were from the east-northeast from the Delmarva to Norfolk, to north-northeast through most of the Chesapeake Bay, creating some low-level convergence in the southern Chesapeake Bay.  The 850 Mb temperatures were still between 6C and 9C, maintaining the >13C temperature difference with the Bay water.  The low-level convergence aided in development of towering cumulus clouds within the bay plume, along with numerous funnel clouds, that did not become waterspouts.  Norfolk International Airport did receive some sprinkles.  The streamer can be seen in radar imagery, and the wind convergence can be seen in the plot of surface observations around Hampton Roads.